(1) Field of the Invention
This invention relates to a printing apparatus and a printing method for printing on an elongate printing medium while transporting the printing medium, and more particularly to a technique for correcting a printing position in a direction perpendicular to a transport direction of the printing medium.
(2) Description of the Related Art
Conventionally, as this type of apparatus there exists an inkjet printing apparatus including a transport mechanism for transporting elongate web paper along a transport path, a plurality of print heads arranged at intervals over the transport path for dispensing ink droplets, edge sensors arranged upstream and downstream of each print head for detecting positions of an edge of the web paper, and a controller operable based on signals from the respective edge sensors for correcting dispense positions of the ink droplets in a direction perpendicular to the transport direction of the web paper (see Japanese Unexamined Patent Publication No. 2016-88654, for example).
With the printing apparatus having such a construction, skewing or meandering is a common phenomenon occurring at the time of transporting the web paper, whereby edge positions of the web paper become displaced in the direction perpendicular to the transport direction. Consequently, with the most upstream print head serving as reference, the ink droplets dispensed from each subsequent print head disposed downstream will shift in the direction perpendicular to the transport direction in response to the displacement of the edge positions of the web paper. Since print quality lowers as a result, the controller determines inking positions by means of linear interpolation based on the signal from each edge sensor, and form prints by shifting the dispense positions of ink droplets in the direction perpendicular to the transport direction.
In Japanese Unexamined Patent Publication No. 2016-88654, the edge sensors are arranged upstream and downstream of each print head, which results in high apparatus cost. Thus, a construction with a reduced number of edge sensors has been proposed (see FIG. 7 of Japanese Unexamined Patent Publication No. 2016-88654).
However, the conventional example having such construction has the following problem.
The conventional apparatus has a reduced number of edge sensors, which lowers the accuracy of inking positions obtained through linear interpolation. Consequently, print positions cannot be corrected appropriately, hence the problem of low print quality.